1. Field of the Invention
This invention relates to an improved vibration absorber for internal combustion engines. More specifically, this invention is directed to an improved vibration absorber assembly for absorbing torsional vibration and altering the moment of inertia of the vibration absorber assembly.
2. Description of Related Art
Internal combustion engines utilize one or more cylinders that operate in a combustion cycle and fire sequentially in order to provide torque to a crankshaft or other output shaft thereby causing rotation thereof to provide power. This power is then used by cars, trucks, boats, generators, pumps, etc.
The power delivered to the crankshaft or output shaft is inconsistent and varies at most of the individual 360 degree points that comprise a single revolution in terms of its components, including torque magnitude and rotation speed. It is not unusual for the torque to deviate from nominal torque by over 100%, and the rotation speed to deviate from nominal by over 15%. These peaks and valleys in torque output result in excessive wear to bearings, gears, clutch plates, universal joints, breakage of component parts such as camshafts, crankshafts, etc., as well as a reduction in power output, and increased fuel consumption.
A typical engine's cyclic power output may be analyzed to further describe the above. An example engine mass produced by a well regarded manufacturer is a 6 cylinder, 4 cycle diesel engine that produces 400 pound foot (hereinafter “lb-ft”) of torque and 50 horsepower (hereinafter Hp) at 800 revolutions per minute (hereinafter “RPM”). The same engine produces 560 lb-ft of torque and 150 Hp at 1400 RPM, and 400 lb-ft of torque and 200 Hp at 2400 RPM.
During each revolution of this engine, three cylinders fire and produce varying amounts of torque upon the crankshaft during their power strokes which occur during 180° of crankshaft rotation. These and all other cylinder firings are timed to occur at 120° increments of the crankshaft's rotation and the power strokes are continuously repeated during the engines operation. Concurrent with these sequenced cylinder firings, various other actions occur such as compression strokes of other cylinders as well as inertial forces of pistons, connecting rods or other components that release energy to or extract energy from the crankshaft. These forces can cause the torque to deviate from nominal torque by over 100%, and the rotation speed to deviate from nominal by over 15% as previously noted, thus yielding characteristics that would obviate the viability of the engine for modern day use.
The addition of a flywheel and/or vibration damper to receive, store, and release some of these torque and power excesses to the crankshaft at a later time in the cycle improves the engine's operating characteristics to a more acceptable 70% deviation from the nominal torque, thus making internal combustion engines commercially viable. The above example engine utilizes a 10.8 inch diameter vibration damper weighing 53 pounds, 22 pounds of which lies in an outer perimeter ring.
In the above regard, engine manufacturers have long incorporated added components such as flywheels, vibration dampers, balance shafts, dampened clutch plates, etc. to improve engine performance by minimizing the negative effects caused by variable torque and rotational speed of the engine. These added components have achieved significant improvement in engine operation via actions and processes outlined hereinafter.
Flywheels have long been used by engine manufacturers to receive and store energy from the crankshaft or other output shaft when the shaft is accelerating, and give back energy to the shaft when it is decelerating. Typically, flywheels are disk shaped with a large proportion of their mass being provided along the rim at a fixed radius from the disk center where the flywheel is generally mounted on the shaft. The quantity of energy stored or released by the flywheel is generally proportional to the rotating shaft's speed change since the location of the mass is fixed.
A vibration damper is like the flywheel in most aspects, yet different insofar as most of its mass is not fixed to a rotating disk, but instead is merely encapsulated, and/or flexibly attached. Because the mass is not fixed, a damper exhibits a dampening or shock absorbing effect upon the torsional vibration of the output shaft, while wasting some of the excess horsepower as heat. In addition, because of the mass of the vibration damper, the vibration damper also acts like a flywheel except that a time delay in response occurs since the mass is not fixed. This device is generally attached to the front of the crankshaft whereas the dampened flywheel is generally attached at the rear of the crankshaft and relies upon a dampening clutch plate, etc., to follow and protect downstream components.
The combined effect of a flywheel and the flywheel effect of the vibration damper have produced significant improvement in engine torque and rotational speed from a nominal but still allow the engine to deviate 70% from nominal in torque output, and 10% from nominal rotational speed. These high deviations from nominal values reduce fuel efficiency and cause component parts excessive wear and failure. Thus, related component parts have to be made stronger to withstand these torque peaks which generally increases cost and weight of the component parts.
Additional inertial mass could be added to further reduce the aforesaid torque deviations. However, this would bring additional negative effects such as engine sluggishness, slow throttle response, accentuated whip-lash action during acceleration reversals, etc. Consequentially, significant addition of inertial mass to vibration dampeners, or other components of the engine have been abandoned as a means to further reduce torque deviations.
U.S. Pat. No. 2,346,972 to Kishline discloses a vibration dampener having a means for dampening torsional vibrations in the crankshaft of an internal combustion engine. In this regard, Kishline discloses that the vibration dampener includes a means for mounting an inertia member on a crank shaft at a point eccentrically disposed with respect to the axis of rotation of the crankshaft. The inertia member is relatively free to move both radially and rotatively with respect to the crank shaft, and to receive energy from, and impart energy to, the crankshaft to produce a dampening effect.
Similarly, U.S. Pat. No. 5,295,411 to Speckhart discloses a system for absorbing torsional vibration in a shaft rotated about an axis that is exposed to torsional disturbances which cyclically increase and decrease the rotational speed of the shaft. In particular, Speckhart discloses a body attachable to the shaft including cylindrical rolling elements positioned within cavities disposed in the body. During operation, the torsional disturbances induce pendulum-like motion of the cylindrical elements within the cavities that absorbs torsional vibration of the shaft. Speckhard further discloses that the cylindrical elements, the cavities, and the torsional disturbances, are related to one another in accordance with an equation which optimizes performance of the system and circumvents time-consuming trial and error techniques during design of the system.
Despite introducing improved systems for absorbing torque deviations, the systems disclosed in Kishline and Speckhart have not gained acceptance in the automotive industry or other applicable industries. Therefore, there still exists an unfulfilled need for a device or method for reducing variation in engine torque and rotational speed. In particular, there still exists a need for such a device and method that more efficiently absorbs torsional vibration and/or alters moment of inertia and flywheel effect of the device. There also further exists an unfulfilled need for such a device or method that increases power output and fuel efficiency of the engine.